Distance measuring device



Marh 29, 1945- CARL-ERIK GRANQVIST 2,371,988

n' l DISTANCE MASURING DEVICE Fild Aug. 2 8, 1941 l i 2 Sheets-Sheet'l Al l 5' lNVENTOR @A 54 March 20, 1945.

CARL-ERIK GRANQVIST DISTANCE MEASURING DEVICE Filed Aug. 28, 1941 2 Sheets-Sheet 2 af-m Patented Mar. 20, 1945 STATES' asusta Dis'rANca MEAsUaiNG DEVICE Carl-Erik Granqvlst, Stockholm, Sweden, as-

-signor to Aga-Baltic Aktiebolag, Stockholm,

Sweden, a corporation of Sweden Application'dugust 28, 1941, Serial No. 408,632 In Sweden ctob'er l, 1940 vi1 claims.

My invention relates to a distance measuring device, andmore particularly to a device for measuring depth or height, which may be used in mediums, such as water and air. It is characterized by high precision and speed of opertion and may be made to produce a continuous indication of the distance directly on an instrument without calculating operations.

The invention will be described below in connection with the annexed drawings, in which Fig. 1 is a block diagram showing the principle of the invention;

Fig. 2 is a time diagram for explanation of this principle;

Fig. 3 is a schematic diagram showing one embodiment of the invention; and

Figs. 4 and 5 are vector diagrams to be used in explaining the operation of the invention.

In Fig. 1 I indicates an oscillator for a preferably ultrasonicfrequency, which is to be used for the measurement. The frequency created by the oscillator Ill is intermittently amplified in the amplifier II and is transmitted by the transmitter I2.

For receiving the wave, intermittently transmitted from the transmitter I2, after its reection, a receiver I 3 is provided, which is in its turn connected to the amplifier It. The amplifier I@ is arranged to control an instrument I5 in such a way, that an indication of the measured distance is obtained.

Both of the amplifiers II and I@ are controlled by an arrangement for determining their times of operation comprising an oscillator I6 producing a variable frequency which is controlled by a tunning condenser I8 having a rotor driven by a continuously rotating motor I'I. The output side of the oscillator I 6 is connected to a, lter I9, preferably of the band pass. The signal wave generated by the oscillator I6 is tapped ol in two different places with different frequency ranges, viz. by means of the conductor 20 from a point with sharp frequency selectivity and also by means of the conductor 2| from a point passing a broader frequency range, as is indicated by means of the schematic indications of frequency selectivity 22 and 23. The conductors 2D and 2| lead each to one rectifier 2d and 25, respectively, the output voltages of which are fed over conductors 2S and 2T, respectively, to the amplifiers II and Iii, respectively, as blocking voltages, being applied in such a way that the amplifier II ig blocked excepting during the times when the filter I9 transmits the signal from the oscillator I5, whereas on the other hand the amplifier I4 is blocked during the time when the signal from the oscillator I5 reaches the amplifier.

Due to the different band selectivity at the points of the filter to which the conductors 20 and 2| are connected, the blocking interval of the amplifier I4 will be somewhat greater than the interval free from blocking, of the amplier The oscillator I6 also is connected to an amplifier 28, which applies Aa voltage to a frequency sensitive discriminator 29, the output side of which is connected to the measuring instrument I5. The amplifier 28 normally is blocked, but this blocking is intermittently cancelled due to the voltage derived from a rectifier 30 when a signal is entering the receiver I3.

The function ofv the arrangement is stated in a time diagram in Fig. 2, in which the time is marked out along thehorizontal axis and the frequency of the oscillator I6 along the vertical axis.

Due to the rotation of the condenser I8 the frequency of the oscillator i6 will periodically pass through predetermined cycles of frequency, as indicated in Fig. 2. It is of no importance to the. principle of this invention, whether these curves have rising or falling characteristics, nor is the shape of the time-frequency curve of importance. It is assumed, for purposes of explanation, that this curve is rising and linear, and that its periodicity is for instance 1,/2 min., as indicated by the scale along the horizontal axis, divided in seconds.

The filter I9 is tuned to a frequency corresponding for instance to that at the point 33. Due to the different selectivity at the points in the filter, where the conductors 20 and 2| are tapped oi, the amplifier I4 is blocked between the points 3I and 35 and the amplifier II is unblocked between the points 32 and 34.

Consequentlya pulse of the ultrasonic frequency from the oscillator I0 is transmitted from the transmitter I2 during the period corresponding t0 the interval from point 32 until the amplier II is blocked again at the. point of time 3ft. One second later the blocking of the amplier IG is cancelled at the point 35.

The receiver I3 is provided for receiving the pulse thus transmitted after its reflection from the surface to which the distance is to be measured. By choosing the points of time for the blocking of the amplifiers I I and I4 as mentioned above the signal received by the receiver I3 dur- I ing transmission of a pulse from the transmitter I2, the said signal consequently'being assumed to be direct instead of reflected, is not amplified. Hence no erroneous registration of this signal takes place. y

The signal of the x'ed frequency of the oscillator I0 is transmitted from the transmitter I2 to the bottom of the sea or the ground surface, where reflection takes place, whereafter the pulse returns and is received by the receiver I3 at a time, which may for instance correspond to the point 41. The signal is amplified in the amplifier I4 and rectified in the rectifier 30, whereupon the direct current voltage obtained in said rectier is supplied to the amplifier 28 in such a way that the blocking of this amplifier is cancelled. The alternating current from the oscillator I6 then will be transmitted through the discriminator 29 to the instrument I5 which thus registers the fre- .quency of the oscillator I6 at the moment of the reflected pulse entering the receiver I3.

From the above it will be evident, that the interval of timebetween the points32 'and 41 will correspond exactly to the time required for the transmitted pulse to pass to the reflection level and back. The frequency in the point 41 therefore will correspond to the distance to the reection level, and consequently this distance can be plotted .on the scale of the instrument I5.

The instrument |5 is assumed to, have no restoring force for its pointer, and therefore this will remain fixed on the position which it has registered until the next pulse affects the adjustment o f the position of the pointer. The instrument therefore will continuously indicate height or depth asthe case may be.

Fig. 3 shows a practical embodiment of the invention.

The oscillator I0 consists of an electronic valve 6| of triodic type. The anode in the valve is connected to the plus terminal of the source 'of voltage, whereas the grid is connected by means of a condenser 62 to the high voltage terminal with respect to alternating currents of an oscillating circuit, which contains the condenser 63 and the coil 64. The low potential terminal of this circuit is connected to ground, whereas a tap 65 is connected to the cathode. The grid, finally, is connected to the cathode over a grid leak 66.

The tap 65 is connected through a condenser 61 to the control grid of electronic valve 68, contained in the amplifier |I, said electronic valve 68 preferably being of screen grid type. In order to control the blocking of the amplifier the grid of the valve 68 is connected by means of a resistor 69 to the conductor 10, corresponding to the conductor 26 in Fig. l. The anode circuit of the valve 68, nally, is connected by means of the primary winding of a transformer 1|, tuned to the frequency of the oscillator I0, to the plus terminal of the mains, and the secondary winding of the transformer 1| is connected by means of coupling condensers 12 and 13 to the transmitter The motor |1 is represented in Fig. 3 at 15. It is fed with current from the mains over a control resistor 16 to make it possible to run the motor at different speeds. The shaft 11 of the motor drives the tuning condenser I8 in the oscillator I6. The` condenser I8 is constructed with small angular extension of its stator part and great angular extension of its rotor part or possibly vice versa, so that the movement of the condenser from the value of capacity corresponding to minimum frequency, to the value of capac-` ity corresponding to maximum frequency, or pos- Finally, the oscillator is arranged to be made A ineffective during the periods of release and return to the position of minimum frequency, for which purpose a cam disc 83 is arranged on the shaft 11 in such an angular position, that it opens and closes a Contact 84 at the respective end positions of the release period.

The oscillator voltage is fed to the different parts shown in Fig. ,1, over a coupling coil 85, which is inductively coupled to the tuning coil 19. Thus a coil 86 is connected to the coil 85, said coil 86 in turn being inductively connected to a primary coil 81 in the filter I9. The coil 81 is connected in parallel to a condenser 88 for tuning the lter to the frequency which is to be transmitted and further it is inductively coupled to a secondary coil 89 which is tuned by means of the parallel condenser 90. The primary circuit, where the selectivity is less, is provided with a mid point tap which is connected to the cathodes of two rectifers 9| and 92, the anodes of which are connected to each end of the primary winding. The cathodes work on a common load resistor 93, shunted for alternating currents by means of a condenser 94. In a similar manner the secondary circuit is connected to two Arectifiers 95 and 96 over a load resistor 91, which is shunted for alternating current by means of a condenser 98.

The load resistor 91 is connected in series with a source ofv voltage 99 in the grid bias conductor 10 of the electronic Valve 68. The magnitude of the source of bias 99 is so chosen, that the electronic valve 68 is normally blocked. This voltage is opposed, however, by the voltage drop over load resistor 91, when a signal is transmitted over the filter 81-88--89--90, whereby a signal is momentarily transmitted from the oscillator I0 over the amplifier and the transmitter I2l (see Fig. l)

The load resistor 93 is connected in opposite direction to the load resistor 91. When a signal is transmitted through the lter 81-88--89-90, an electronic valve |00 will therefore momentarily be blocked. This electronic valve is connected to be fed with the signals which may be received by a receiver I3. The signals are transferred by means of the transformer |02 to the grid circuit of the electronic valve |00, which contains the grid condenser |03 and the grid leak |04, this last named being connected to the negative terminal of the load resistor 93.

The electronic valve |00 is connected through the transformer |05 to the rectifiers |06 and |01, which work in the same manner as the earlier described retiers and create a blocking voltage in the load resistor |08, which is shunted for alternating current by the condenser |09.

The load resistor |08 is connected in series with the source of voltage I0 to the grid conductor of an electronic valve the source of bias being polarized in such a Way that the electronic valve is normally blocked, the blocking bias being opposed, when a signal is received in the receiver I3. The grid of the valve is connected with respect to alternating currents to the coil over a grid condenser I2 and is provided with a grid.

lead ||3. The output conductor of the electronic 2,371,988 vvvalve III is connected by means of avfcondenser I I4 to a grid of an electronic valve IIB, contained in the discriminator 29, said grid being provided f with a grid leak |I6. The output circuit of this eiectronicva'lve Ils, nnauy, is'fconnected to a connected between the high voltage terminal' with respect to alternating current of the coil I I1, on the one side, and themid point of the coil H9, on the other side. The last named secondary coil, nally, is tuned by means of a variable condenser |2I, the shaft of which is driven lby the differential motor |22 and controls in its turn the pointer of the instrument I5.

The two ends of the secondary side H9 are connected through parallel resistors |24 and |25 and series resistors |26 and, |21 to rectiers I3| and |32, respectively. The junction point of the resistors |26 and |21 is connected-to ground by` means of a bias battery |28, whereas the ends of the resistors |26 and |21 are -connected to the grids of the direct current amplifier valves |29 and |30. The anode circuits of these direct current amplifier valves are connected to the differential windings of the motor |22. 1 It is assumed that the operation of the above described arrangement' for measuring distances is lsuiliciently clear from the description of Fig. 1. The operation of the discriminator 29, however, is set forth more in detail as follows:

The amplifier 28, represented in Fig. 3 by the valve IH, is blocked during normal function, but is momentarily -unblocked when a signal enters the receiver I3 after reflection against the re` flection medium, the distance of which is to be determined. vAt this moment the oscillator has a predetermined frequency lying between its maximum value and its minimum value, and this frequency is determined by theelapsed time from the moment when the signal was transmitted by means of the transmitter i2. By measuring this frequency one can obviously determine the time for the sound to pass through the medium and back, or in other Words, one can determine the distance to' the point of reflection.

The signal from the oscillator valve=86 at the frequency in question now is amplied by= the valve H5, contained in the discriminator, and is fed to the output transformenwhich is of a special kind for this type of discriminators. Its function is based on the following principle.

At exactly correct tuning the voltage OP (Fig. 4) in the primary circuit ||1 and the voltage SS in the secondary circuit ||9 in the tuned transformer are mutually displaced in phase 90 as indicated by the lines SS and YOP in Fig. 4. If the voltage OP is added vectorially to the two halves OS and OS of the voltageSS' two congruent vectors OA and OA.' 'are obtained, which are mirror images of each other and are equal. If they are rectified two equally great direct current voltages are obtained, which, if they ar opposed will give the resultant O.

If, however, the tuning should not be exactly correct, the voltage vector of the secondary winding is displaced in relation to the voltage vector of the primary winding' as indicated by the vector OP' (Fig. 5), so that these vectors are nolonger in 90 mutual phase position. The consequence thereof is. that one of the resultants OB obtained by the vectorial addition, will be greater. whereas the'other vector 0B' decreases,

and vconsequently also thedirect currentvoltages obtained `by the rectification are of different magnltudes, so that they'no longer compensate each other. A resultant' direct-current voltage will therefore arise, the polarity of which is determined by the direction of the error in frequency l which caused the error in phase and the magmtude of which is, at least at small errors in frequency, practically proportional to the error in frequency. i

The resultant voltage can therefore be' used in order to reestablish the frequency balance in the system'. 'I'his takes place in the form of the present invention' shown in Fig. 3, by feeding the resultants of the voltages, vectorially added in the transformer ||1I|9, to rectiers |3| and |32, the output ldirect current voltages of which are fed to grids in the direct current amplifying valves |29 and |30 as control voltages. The anode currents of these valves may therefore be approximately proportional each to one of the emanating vectoriall resultants, and they are fed y. each to one ofthe windings in the differential motor |22, counteracting each other.

When a frequency error and an error in phase,

cause thereby,.occurs, one of the windings in the motor |22 will therefore magnetically overbalance, so that the motor is put in rotation inthe direction to cause condenser I2| to shift the tuning frequency of the transformer I|1| I8' in a direction to balance the frequency. When frequency balance is achieved balance between the fields of both windings of the differential motor is also obtained and consequently the motor will stop. The position of the condenser, however, is on the one hand a measure of the tuning fre-v quency of the transformer, and on the other hand it is a measure of the frequency of the'oscillator i6, Fig. 1, at thggnoment when the amplifier 28 is unblocked, as it is this frequency which is fed to the discriminator. V'I'he instrument I5, connected to the shaft of the condenser |2I, therefore will, each time a pulse is received. intermittently adjust its tuning to a, position which corresponds to the time of receipt of the pulse or in other words to the distance to the level of reiiection.

Of course lt may happen that the distance to the level of reflection is so great that the total time of travel of a pulse from the transmitter to the reflection level and back to the receiver is longer than the time, for instance half a minute, between pulses. an error corresponding to the time of movement of halfv a minute. In order to avoid this at exceptionally great distances the resistor 16 may bedecreased to a value at which the motor 15 is moving with half the speed, one thirdof the speed and so on and the indications of the instrument I5 may be increased by the same factors. vIn a similar way at exceptionally/ small distances the speedv of the motor may be increased, whereby the extent of movementof the instrument may be utilized to obtain a higher gree of precision.

Of course the invention is not klimited to the embodiment shown and described in detail above .but substantial modifications thereofl may be made.

Thus it may be suitablevnot Yto give-the condenser |8 such a shapethat Athe frequency charcision is obtained over the entire measuring.

The instrument then may show Y range. It is of course not necessary that the measured distance be registered on an instrument, but the registration may assume other forms, for instance the giving of an alarm signal when the distance decreases below a predetermined limit value and so on.

What is claimed:

1. A device for measuring distance, comprising a wave transmitter, a wave receiver responsive to waves propagated from said transmitter after reflection from the surface the distance to which is to be measured, a source of alternating current of variable frequency, means causing said frequency to vary cyclically over a predetermined band, means rendering said transmitter operative while said frequency passes through a predetermined portion of said band, a frequency responsive device connected to be responsivelto the instantaneous frequency ofsaidsource and means actuated by said receiver in response to received energy to render said frequency responsive device operative, said system being so constructed and arranged that the frequency thus indicated by said frequency responsive device serves as a measure ofthe timing between the transmitted and received pulses.

2. A device for measuring distance as set forth in claim 1, in which the means for rendering the transmitter' operative comprises a band-pass iilter connected to pass saidpredetermined portion of said `band of frequencies, and including means actuated by the energy passed by said filter for controlling the operation of said transmitter.

3. A device for measuring distance as set forth in claim 1, in which the wave transmitter includes a .normally blocked amplifier and including a band-pass filter connected to pass said predetermined portion of said frequency band and means actuated in response to energy passed by said filter to unblock said amplifier.

4. A device for measuring distance as set forth in claim 1 in which frequency responsive means is arranged to render said receiver inoperative While said frequency passes through a portion of said band including said first mentioned predetermined portion, so that a reception of waves propagated directly from said transmitter is prevented.

5. A device for measuring distance as set forth in claim 1, including a band-pass filter connected to pass a predetermined portion of the band of frequencies from said source, means responsive to the energy passed by said filter to render said transmitter operative, a second band-pass filter connected to passa wider band of frequencies than said rst filter, said last band containing the first band and means responsive to energypassed by said-second filter to render said receiver inoperative whereby the receiver is rendered inoperative during the periods of operation of said trans-V niitter.

6. A device for measuring distance as set forth in claim 1, in which the frequency responsive device comprises a tuned circuit having a variable tuning element, a differential motor connected y to be Vactuated in accordance with an unbalance produced in said tuned circuit by energy of dif- 4' ferent frequency from the frequency to which said circuit is tuned. said motor being connected to actuate said tuning element in a direction to tune saidl circuit to the frequency -of the applied energy. indicating means actuated by said motor and means actuated in response to energy received by said Wave receiver to render said frequency responsive device operative, whereby said device is caused to indicate the frequency of said source at the instant energy is received by said wave receiver. l,

7. A device for measuring distance as set forth in claim 1, in which amplifiers are provided in said transmitter and in said receiver, and including filter means connected to pass predetermined portions of said band of frequencies from said variable frequency source, means rectifying the energy passed by said filter means to produce direct current voltages, and means controlling the operation of said amplifiers by said last voltages.

8. A' device for measuring distance as set forth in claim 1, in which amplifiersare provided in said transmitter and in said receiver, and including filter means connected to pass predetermined portions of said band of frequencies from ysaid variable frequency source, means rectifying the energy passed by said filter means to produce direct current voltages, means connecting the transmitter amplifier to be normally blocked and means connecting the receiver'amplifier to be normally iperative, and means applying said voltages in a sense to unblock said transmitter amplifier and to block said receiver amplifier.

9. A device for measuring distance as set forth in claim 1, in which amplifiers are provided in said transmitter and in said receiver, and including filter means connected to pass predetermined portions of said band of frequencies from said variable frequency source, means rectifying the energy passed Vby said filter means to produce direct current voltages, means connecting the transmitter amplifier to be normally blocked and means connecting the receiver amplifier to be normally operative, and means applying said voltages in a sense to unblock said transmitter amplifier and to block 'said receiver amplifier,

- said voltages being applied to block said receiver amplifier over a period longer than and overlapping the period of operation of said transmitter.

10. A device for measuring distance as set forth in claim 1, in which the frequency responsive device comprises a tuned circuit having a variable tuning element. a diierenttial motor connected to be actuated iii accordance with an unbalance produced in said tuned circuit by energy of different frequency from the frequency to which said circuit is tuned, said motor being connected to actuate said tuning element in a direction to tune said circuit to the frequency of the applied energy, indicating means actuated by said motor and means actuated in response to energy received b said wave receiver to render said frequency responsive device operative, whereby said device is caused to indicate the frequency of said source at the instant energy is received by said wave receiver, and control means controlling the speed of operation'of said differential motor so as to vary the range of indication of said frequency responsive device.

11. The device for measuring distance as set forth in claim 1, in which said frequency is caused to vary over said band as a substantially logarithmic function of time, whereby the precision oi measurement is made uniform over the entire operating range.

. CARL-ERIK GRANQVIST.

Certificate of Correction Patent No. 2,371,988. March 2o, 1945.

' CARL-ERIK GRANQVST It is hereby certied that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 1, rst column, line 39, after pass insert type; page 3, second column, line 27, :for cause read caused; and that the said Letters Patent should be read With these corrections therein that the same may conform to the record of the case in the Patent Olice.

Signed and sealed this 3rd day of September, A. D. 1946.

LESLIE FRAZER,

Fz'nst Assistant ommz'ssz'oner of Patents. 

